re: re. Correct me if I'm wrong but it
Actually I think everyone forgot to answer Johannes as to why a 250W/kg nuclear reactor was actually more efficient than he thought.
First of all, its 250 W/kg of reactor, not fuel (...). That means a 1 ton rector should produce 250 kW. We are not talking about 1 ton of Uranium, which produces much more enrgy than that.
Secondly, fission reactions involve only a very small amount of mass loss, whihc is converted to energy by Einstein's equation (e-mc2). We haven't yet mastered matter-anti-matter reactors therefore we are not able to fully convert mass into energy.
Obtaining 250W/kg of reactor is not inefficient at all in this day and age, its actually quite good.